Mass spectrometer tube housing assembly



y 1956 w. A. MORGAN 2,756,340

MASS SPECTROMETER TUBE HOUSING ASSEMBLY Filed April 29, 1954 [/7 van $0.2" h/a/'er' .77. Mar 677 1 /715 fitter-r1 ey United States Patent MASS SPECTROMETER TUBE HOUSING ASSEMBLY Walter A. Morgan, Latham, N. Y., assignor to General Electric Company, a corporation of New York Application April 29, 1954, Serial No. 426,340

6 Claims. (Cl. 250-413) This invention relates to mass analyzing instruments, and more particularly to a housing assembly for a mass spectrometer tube.

In the mass spectrometer, a gas sample to be analyzed is bombarded by an electron beam to produce ions in an ionization chamber, and the ions thus formed are separated into various components having different massto-charge ratios by subjecting them to the influence of electric and/or magnetic fields. This separation is generally achieved in an analyzing section where the individual components are directed upon an ion collector and discharged, and the intensity of the resultant ion current is measured. The several components of the sample may be caused to fall successively upon the collector by varying the electric and/or magnetic field, and the nature and proportions of the components can then be determined.

Various types of mass spectrometers are well-known in the art, and one such instrument is disclosed in the co-pending application of George Jernakoff, S. N. 369,169, filed July 20, 1953, and entitled Radio Frequency Mass Spectrometer, Patent No. 2,698,389. This particular instrument utilizes for ion separation 21 magnetic field that is perpendicular to an alternating electric field; and the electric field has a frequency of alternation corresponding to the natural frequency of ions having a desired mass. These fields effect the separation of the ions having the desired mass from those having other masses. In order to effect this separation, there is provided an ionization chamber, an electron beam source for ionizing samples of matter introduced into the chamber, apparatus for producing a magnetic field across the chamber, and apparatus for producing an alternating electric field at right angles to the magnetic field and having a frequency corresponding to said natural frequency of the ions having the desired mass. The instrument further includes a probe for collecting the ions accelerated in the above described manner. This particular instrument is called an ion resonance spectrometer in the art.

The present invention is concerned with a housing assembly for the ionization chamber of analyzer section of a mass analyzer, and more particularly with a housing assembly especially adapted for use with an ion resonance mass spectrometer. This invention is intended to achieve a uniform magnetic field within the housing assembly by means of a simple mechanical structure, to provide the maximum magnetic field strength within said assembly for any given magnet, and to enable the spectrometer tube parts to be inserted therewithin and be readily aligned relative to the housing so as to eliminate any need for adjusting any of the dimensions of the housing.

It is, therefore, one object of this invention to provide a housing assembly for a mass analyzer in which a uni form magnetic field strength can be readily obtained.

It is another object of this invention to provide a housing assembly for a mass analyzer in which there is Patented July 24', 1956 achieved a maximum magnetic field strength for any given magnet.

It is a further object of this invention to provide a housing assembly for a mass analyzer within which the mass analyzer tube elements may be inserted and be readily aligned, and which greatly simplifies the construction of the mass spectrometer tube.

Other objects and advantages will appear as the description of the invention proceeds.

in accordance with the invention, there is disclosed a housing assembly for a mass analyzer for achieving the foregoing objects and advantages. This housing assembly includes an enclosure, which in the present form of theinvention contains the main elements of an ion resonance mass spectrometer tube, having two opposed open ends therein, and a pair of magnetic pole pieces respectively closing the respective ends of the enclosure and joined thereto by a vacuum-tight weld. The pole pieces complete the enclosure and form a part thereof. Further, the enclosure has a lip thereon adapted to receive the base of a tube element assembly to be inserted within said enclosure, the base and the lip having holes therein through which dowel rods are inserted so that the tube elements are correctly aligned with the pole faces when they are so inserted within the enclosure. By means of this construction, it is possible to ensure, prior to the assembly of the mass spectrometer tube, that the faces of the pole pieces will be perfectly parallel and as close together as will permit the tube elements to be inserted therebetwcen. Thus, when the mass analyzer tube elements are inserted into the housing assembly through the aforementioned aperture, they are readily aligned relative to the pole pieces, the faces of the pole pieces are perfectly parallel and thus ensure a uniform magnetic field, and the faces of the pole pieces are as close together as is practical and thus ensure a maximum magnetic field strength within the ionization chamber.

The features of this invention which are believed to be novel and patentable are pointed out in the claims which form a part of this specification. For a better understanding of the invention, reference is made to the drawing wherein there is shown a single figure giving a perspective view of the invention with a portion thereof cut away in order to show its interior.

Referring now to the sole figure, there is shown an enclosure 1 having a pair of opposed open ends 2 and 3 therein. This enclosure is made of stainless steel and is preferably cylindrical in form. Closing the respective ends 2 and 3 of the enclosure, are a pair of magnetic pole pieces 4 and 5, respectively. These pole pieces may be made of a magnetic material such as soft iron, and their internal and external faces are nickel plated in order to prevent them from being subject to rust. Pole pieces 4 and 5 are adapted to tightly close enclosure ends 2 and 3, respectively, and they are welded thereto along the edges by means of a vacuum-tight weld in a manner well-known in the art.

Enclosure 1 also contains an aperture 6 therein through which mass analyzer tube elements are inserted. As shown in the drawing, these elements comprise a filament 7 for emitting electrons, a plate 3 containing a slit therein for defining the electrons emitted by filament 7 into a beam, six slotted electric field producing plates labelled 9, all disposed within a frame 10, and an electron collector plate 11. Elements 7, 8 and 11 form an electron gun; and When a magnet is applied across the outer surfaces of pole pieces 4 and 5, said magnet and pole faces serve to produce a magnetic field which guides the electrons from cathode 7 to electron collector 11, the electrons being formed into a beam 13, as shown.

Enclosure 1 is also provided with an aperture 14 through which samples to be analyzed within the mass spectrometer housing assembly are applied. Samples such as gases are caused to enter aperture 14 into enclosure where they are ionized by electron beam 13. Applied to plates 9 are alternating potentials placed thereupon by leads which have been omitted so as not to obscure the drawing, and these potentials together With'a magnetic field applied across pole pieces 4 and 5 cause the ions to assume a rotary spiral motion through the slots in plates 9. At one point in this spiral motion, these ions impinge upon an ion collector which is inserted through an aperture 16 Within enclosure 1 adjacent to an end plate of plates 9. Ion collector 15 is connected to the remainder of the mass spectrometer, not shown, to provide an indication of the particular element corresponding to the natural frequency of the ions within the assembly. Enclosure 1 also includes an aperture 12 at which is applied a pump for continuously evacuating the housing assembly thus continuously changing the samples within the assembly.

Attention is now directed toward aperture 6. This aperture has a lip 17 thereon within which is a pair of dowel rods 18. All of the leads from cathode 7, plates 8 and 9, and electron collector 11 are attached to a base not shown, which has a lip corresponding to lip 17 thereon. Therefore, by merely inserting the tube elements within aperture 6 and then inserting dowel rods 13 within the two lips, the entire internal assembly within the enclosure 1 is aligned relative to pole faces 4 and 5. This alignment is so chosen that electron beam 13 i at right angles to the inner surface of pole faces 4 and 5. Moreover, in assembling enclosure 1, care is taken to ensure that the pole faces of 4 and Bare perfectly parallel.

By means of the foregoing extremely compact construction, the pole piece faces are caused to be perfectly parallel, thus ensuring a uniform magnetic field; the pole faces themselves are extremely close together, being separated by an amount barely sufficient to enable the internal portions of the mass analyzer to be inserted, thereby causing the field strength within the enclosure to be a maximum for any magnet placed across pole pieces 4 and 5; and due to the dowel rods, the internal portions of the mass analyzer are caused to be correctly and quickly aligned with said pole pieces. Hence, the construction greatly simplifies manufacture of the mass spectrorneter.

It should be emphasized that although the housing assembly of the invention has been illustrated in connection with an ion resonance type of mass spectrometer, this compact structure is not limited to such an instrument type. The assembly may also be used to house the ionization chamber or resolving section of any mass spectrometer type and all of the foregoing enumerated advantages will still attach to the resultant instrument.

While there has been described what is at present considered a preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention; and it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A housing assembly for the tube elements of a mass analyzer, comprising an enclosure for said elements having two opposed open ends therein, and a pair of magnetic pole pieces having parallel inner faces and respectively closing the respective ends of said enclosure, said pole pieces being joined to said enclosure by a vacuumtight weld and completing said enclosure by forming 'a part thereof, said enclosure having an opening in a side thereof between said pole pieces adapted to receive the electron beam producing tube elements when they are inserted within said enclosure, and means on said enclosure proximate said opening adapted to cooperate with a base for said electron beam producing tube elements to align the electron beam at right angles to said parallel inner faces of said pole pieces.

2. A housing assembly for the tube elements of a mass analyzer, comprising a cylindrical enclosure for said elements having open ends therein, and a pair of magnetic pole pieces having parallel inner faces and respectively closing the respective ends of said enclosure, said pole pieces being joined to said enclosure by a vacuum-tight weld and completing said enclosure by forming a part thereof, said enclosure having an opening in the side thereof between said pole pieces adapted to receive the electron beam producing tube elements when they are inserted within said enclosure, and external means on said enclosure proximate said opening adapted to cooperate with a base for said electron beam producing tube elements to thereby align the electron beam at right angles to said parallel inner faces of said pole pieces.

3. A housing assembly for the tube elements of a mass analyzer, comprising a cylindrical enclosure for said elements having open ends, and a pair of magnetic pole pieces having parallel inner faces and respectively closing the respective ends of said enclosure, said pole pieces 7 being joined to said enclosure by a vacuum-tight weld and completing said enclosure by forming a part thereof, said enclosure having an opening in the side thereof between said pole pieces adapted to receive the electron beam producing tube elements when they are inserted within said enclosure, mounting means proximate said opening to support said electron beam producing tube elements, and means associated with said mounting means to engage said base so as to align the electron beam at right angles to said parallel inner faces of said pole pieces.

4. A mass analyzing instrument comprising a tube element assembly including means for ionizing samples of matter introduced within said assembly and a plurality of slotted plates for separating ions of a given natural frequency from ions having another natural frequency, an enclosure for said assembly having opposed open ends therein, and a pair of magnetic pole pieces having parallel inner faces and respectively closing the respective ends of said enclosure and joined thereto by a vacuum-tight Weld, said pole pieces completing the enclosure and forming a part thereof, said enclosure having an opening in a side thereof between said pole pieces adapted to receive said tube element assembly, and means on said enclosure proximate said opening adapted to cooperate with a base for said tube element assembly whereby said tube element assembly is aligned relative to the inner faces of said pole pieces.

5. A mass analyzing instrument comprising a tube element assembly including means for ionizing samples of matter introduced within said assembly and a plurality of slotted plates for separating. ions of a given natural frequency from ions having another natural frequency, an enclosure for said assembly having opposed open ends therein, and a pair of magnetic pole pieces having parallel inner faces and respectively closing the respective ends of said enclosure and joined thereto by a vacuum-tight weld, said pole pieces completing the enclosure and forming a part thereof, said enclosure having an opening in a side thereof between said pole pieces adapted to receive said tube element assembly, supporting means on said enclosure proximate said opening adapted to receive a base for said tube element assembly, and means associated with said supporting means adapted tohold said tube element assembly aligned relative to the inner faces of said pole pieces. v

6. A mass analyzing instrument comprising a tube element assembly including electron beam producing means for ionizing samples of matter introduced within said assembly and a plurality of slotted plates for separating ions of a given natural frequency from other ions having another natural frequency, an enclosure for said assembly having opposed open ends therein, and a pair of magnetic pole pieces having parallelinner faces and respectively closing the respective ends of said enclosure form an electron beam at right angles to said parallel and joined thereto by a vacuum-tight weld, said pole inner faces.

pieces completing the enclcsure and forming a part thereof, said enclosure having an opening in a side References Citedinthe file Of this Patent thereof between said pole pieces adapted to receive said 5 UNITED STATES PATENTS tube element assembly, means proximate said opening adapted to cooperate with a base for said tube element fig assembly whereby said tube element assembly is aligned as um relative to the inner faces of said pole pieces so as to 

